The purpose and operation of a basic shock absorber is well known. See Crouse & Anglin, Automotive Mechanics (10th Ed.), McGraw-Hill (1993), at Chapter 49, and Haney & Braun, Inside Racing Technology, TV Motorsports (1995), at Chapter 5, both of which are incorporated herein by reference.
In general, the suspension springs support the weight of the vehicle and its load, and absorb road shocks. The shock absorbers help control or dampen spring action to avoid spring oscillation and assist in maintaining control of the vehicle, and as a result, are often referred to as "dampers." When a car moves over a bump in the road, the wheel moves up with the bump and back down on the other side of the bump. The spring and damper compress as the wheel moves up, in a mode referred to as "compression." After passing the bump, a correctly designed spring and damper system goes through a small degree of oscillation in return to its steady state condition, in a mode referred to as "rebound." Ideally, the damper will not only control oscillation, but also prevent the spring from achieving either full compression or full extension. Full compression would indicate that the vehicle's suspension system is "bottomed out." Full extension would mean that the vehicle's suspension system is "floating," and no longer in contact with the road. Thus, a well designed spring/damper system allows the vehicle chassis to remain relatively steady, and keeps the tires in contact with the ground despite bumps or holes in the road and forces caused by cornering or changes in the vehicle's speed.
In high performance applications, such as in automotive racing, the springs and dampers are considered one of the more important tunable systems on the vehicle, and one that can greatly affect the vehicle's handling characteristics. Indeed, adjusting the damper characteristics can dramatically improve the way a vehicle performs when turning around a comer, under acceleration and during braking.
More specifically, most modern dampers include an oil-filled cylinder or tube in which a piston moves up and down in response to movement of the wheel relative to the vehicle chassis. The piston typically divides the cylinder into upper and lower fluid chambers. The movement of the piston forces oil or hydraulic fluid in the cylinder to flow through small fluid passages or orifices in the piston. The orifices in the piston are typically restricted by spring-loaded check valves or disks that deflect under pressure. The resulting fluid friction limits both compression and rebound. The more easily the fluid flows through the holes, the softer the ride. In contrast, smaller holes and stiffer check valves or deflection disks, have greater restriction and provide a stiffer ride. Thus, varying the size of the orifices, or the stiffness of the valves or deflection disks, alters the rebound and compression characteristics of the spring/damper system, and changes the ride characteristics of the vehicle. For high performance applications, such adjustability is greatly desired, particularly if the rebound and compression settings can be independently and easily changed.
Many different techniques are known for adjusting damper settings. For example, it is known to change performance characteristics of a damper by removing the damper from the vehicle and disassembling it to: change the number, diameter, order and thickness of the deflection disks; substitute a piston with different size, shape and number of orifices; substitute check-valves with different loading; etc. However, removing a damper from the vehicle and disassembling it to change its internal components is both complicated and time consuming, and therefore, is undesirable. Thus, dampers were developed having external adjustments that move internal parts to change the flow restrictions in the piston or some other metering orifice, or the preload on check valves or deflecting disks. Examples of such adjustable dampers can be found in the identified texts incorporated above, and in U.S. Pat. Nos. 4,220,228, 4,313,529, 4,337,850, 4,463,839, 4,476,967, 4,800,894, 4,880,086, 4,958,706, 5,133,434, 5,402,867, 5,409,090, 5,542,509, each of which is also incorporated herein by reference.
As variously disclosed in the above references, most externally adjustable shock absorbers are complex and expensive to manufacture and maintain, and in addition, require the separate adjustment of multiple orifices, valves or deflection disks.
For example, in U.S. Pat. No. 5,402,867, a guide member is provided with separate rebound and compression guide ports, and a cooperating shutter is provided with separate rebound and compression shutter ports. By rotating the shutter within the guide member, the degree that the guide and shutter ports are "opened" or "closed" is changed, thereby altering the resistance to the flow of oil as the piston moves. However, in the '867 Patent, the rebound and compression strokes are not independently controlled. Instead, as the "rebound" ports are closed, the "compression" ports are opened. Likewise, as the "rebound` ports are opened, the "compression" ports are closed. Thus, the user can not independently set rebound and compression, thereby limiting the degree of adjustment to the damping characteristics. See also U.S. Pat. No. 5,409,090, which is similarly limited in adjustment of the rebound and compression characteristics.
U.S. Pat. No. 4,800,994, purports to provide a damper in which the rebound and compression characteristics can be set independently from each other. However, as with the '867 patent, a shutter and guide cooperate to provide three settings that simultaneously adjust the rebound and compression. Thus, it is again not possible to adjust rebound settings without also affecting the compression settings, and vice-versa.
In U.S. Pat. No. 4,337,850, still another shutter and guide arrangement is shown, with a plurality of settings between a fully closed and fully open position. An adjusting knob incorporating a spring-loaded check ball maintains the selected alignment between the shutter and guide. The adjusting knob includes markings to visually indicate the selected setting. However, once again, the compression and rebound settings cannot be set or adjusted independently, without simultaneously affecting each other. See also U.S. Pat. No. 4,220,228 which shows a similar system, and U.S. Pat. No. 4,313,529, which shows an electronic adjustment control for a shutter and guide type of system.
U.S. Pat. No. 4,476,967 discloses a damper including a bore formed in the piston rod, and having an orifice and cooperating tapered needle member in its lower end forming a passage between the upper and lower oil chambers. The oil flow through the passage during movement of the piston can be adjusted by axially displacing an adjustment rod to move the tapered needle relative to the orifice. By axially lowering the tapered needle relative to the orifice, the flow of oil is reduced, and conversely, by axially raising the tapered needle, the flow of oil is increased. The mechanism for adjusting the flow characteristics includes axially extending ridges that cooperate with a spring-loaded check ball to provide "click stops" for axially adjusting the needle. A visual indicator or scale is provided on the outer circumference of a dial member for visually indicating the adjusted position of the needle in the orifice. However, as with the shutter and guide arrangements discussed above, the '967 Patent fails to provide any mechanism to independently adjust the rebound and compression settings. See also, the text Inside Racing Technology, identified above, which discusses at page 168 a double-adjustable Penske shock that uses an adjustable needle valve to vary rebound settings. However, there is no discussion regarding how the compression settings of the Penske shock are adjusted.
U.S. Pat. No. 4,958,706 purports to disclose an adjustable damper incorporating separately adjustable rebound and compression settings. The damper is described as including two separate manual rebound adjusters, one each for low speed and high speed characteristics. The high speed rebound adjustment is supposedly made by rotating a knob to lower or raise an adjustment rod to limit the amount a bypass valve can open. The low speed rebound adjustment is purportedly achieved by rotating a second knob to rotate the adjustment rod to change the bias on the bypass valve. The compression characteristics of the damper are also said to be adjustable by a separate manual adjuster, preferably on a separate reservoir. Two alternate embodiments are also briefly described in which one knob is said to be used to achieve linear displacement of the adjusting rod in the tubular piston rod to adjust compression, and the second knob is used to adjust either the high speed or low speed rebound characteristics. In the latter embodiments, a cup-shaped valving member has a tapered valving surface which cooperates with an annular manifold in the piston. The degree to which the tapered valving surface of the cup-shaped member extend into the annular manifold controls the compression rate characteristics of the damper. The adjustments are all made manually by turning knobs. However, the devices of the '706 Patent are both complex and expensive to manufacture, and correspondingly difficult to maintain and use reliably.
U.S. Pat. No. 5,133,434 shows a damper that is independently adjustable in rebound in compression. A first adjustment knob is used to rotate an actuating rod to turn a spring seat and thereby adjust the bias on a rebound disk valve. A second adjustment knob is used to rotate an adjustment rod to align orifices of different size to vary the rate of flow to the compression valve. A second embodiment is also shown in which both the compression and rebound characteristics are adjusted by rotating separate rebound and compression rods to vary the path area in corresponding throttling orifices in the rebound and compression valves. However, the system of the '434 Patent relies on a complex and expensive arrangement of radial paths, grooves and throttling ports.
Thus, the need exists for a high-performance damper or shock that is easily and independently adjusted in both rebound and compression, that is effective and reliable, and that is easily and economically manufactured.